Girlfriend having sex?

my girlfriend 17 and im 16 have been dating about 2 months and she told me she wants to have sex with me really badly. we fell in love with each other fast and were happy together. Her sister is overprotective so doing it there is not possible. My place there is no privacy like my mother like wont let me close my bedroom door fully. i have a basement but she goes down there. We makeout and i feel her up like but i want to have sex with her. any tips on how because its basically not possible. ?